linux-kernel - 答复: [PATCH] x86: move turbo_disabled() out of intel_set_max_freq

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Date:   Wed, 29 Apr 2020 08:53:20 +0000
From:   "Li,Rongqing" <lirongqing@...du.com>
To:     Giovanni Gherdovich <ggherdovich@...e.cz>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rafael.j.wysocki@...el.com" <rafael.j.wysocki@...el.com>
Subject: 答复: [PATCH] x86: move turbo_disabled() out of intel_set_max_freq_ratio


> Hello,
> 
> the problem is that turbo can be enabled/disabled by the firmware at runtime,
> after the machine has booted.
> 
> This happens for example with the Dell XPS 13, where turbo gets disabled by
> the firmware if the machine is disconnected from AC power and runs on battery.
> The laptop could boot on battery (turbo disabled), then after some time the
> user connects the AC power supply, turbo gets enabled, and with your patch
> we wouldn't know what is the turbo_freq/base_freq ratio to do frequency
> invariance (we skipped reading MSR_TURBO_RATIO_LIMIT at boot because
> turbo was disabled at that timed).
> 
> This behavior was requested by reviewers in this thread:
> https://lore.kernel.org/lkml/1906426.HDqaVa71mF@kreacher/
> and implemented with 918229cdd5ab ("x86/intel_pstate: Handle runtime turbo
> disablement/enablement in frequency invariance").
> 


Thanks for you explanation

Sorry for noise

-Li

> 
> Thanks,
> Giovanni Gherdovich